The intent of the proposed research is to further the understanding of ribosomal DNA in the acellular slime mold Physarum polycephalum. The properties of these extrachromosomal genes make them a model system for investigating some of the general features of eucaryotic genes, and perhaps of eucaryotic chromosomes. The research has four major goals: The first is to determine the nucleotide sequences of several important regions of the rDNA, including origins of transcription and replication and binding site for a regulatory protein. The second is to define more clearly the functions that the replication origins near the center of the rDNA, and the gapped DNA sequences near the ends of the linear rDNA have in the replication process. Knowledge of the structure of the origins and of the rDNA ends may provide insight into the initiation of eucaryotic DNA replication and into the structure of chromosomal telomers. The third is to clarify the mechanism underlying the uniparental, non-Mendelian inheritance or rDNA that we have observed recently in genetic crosses. It appears from the genetic results that the several hundred rDNA molecules all must derive from a single molecule at some stage of the life cycle. The fourth goal is to contribute to the understanding of the function of ornithine decarboxylase in regulating rDNA transcription. This enzyme has been found by others to become phosphorylated, to bind to rDNA, and to stimulate transcription in a polyamine-sensitive manner.